add domains readme (#35)

pallets/domains/README.md

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+# Domains Pallet
+
+Domains pallet allows users to register and manage domains.
+
+
+## Resolving Domain Names
+- **Pallet Name:** domains
+- **Storage:** `RegisteredDomains`: `DomainName` => `DomainMeta`
+
+Domain name can be resolved to obtain the owner.
+
+
+In addition to resolving a domain owner, you can also resolve the various records set up
+by the user. The following table shows a list of records that can be attached to the domain name.
+
+
+<table>
+<thead>
+  <tr>
+    <th>Record Name</th>
+    <th>Type</th>
+  </tr>
+</thead>
+<tbody>
+  <tr>
+    <td rowspan="3">Content</td>
+    <td>String</td>
+  </tr>
+  <tr>
+    <td>IPFS</td>
+  </tr>
+  <tr>
+    <td>Hypercore</td>
+  </tr>
+  <tr>
+    <td rowspan="3">InnerValue</td>
+    <td>Subsocial Account</td>
+  </tr>
+  <tr>
+    <td>Subsocial Space</td>
+  </tr>
+  <tr>
+    <td>Subsocial Post</td>
+  </tr>
+  <tr>
+    <td>OuterValue</td>
+    <td>String</td>
+  </tr>
+</tbody>
+</table>
+
+### The full domain metadata recorded for each domain
+```rust
+pub struct DomainMeta<T: Config> {
+    /// When the domain was created.
+    created: WhoAndWhenOf<T>,
+    /// When the domain was updated.
+    updated: Option<WhoAndWhenOf<T>>,
+
+    /// Specific block, when the domain will become unavailable.
+    expires_at: T::BlockNumber,
+
+    /// The domain owner.
+    owner: T::AccountId,
+
+    /// Some additional domain metadata. For example avatar and description for this domain.
+    content: Content,
+
+    /// The inner domain link to Subsocial entity such as Account, Space, or Post.
+    inner_value: Option<InnerValueOf<T>>,
+
+    /// The outer domain link (any string).
+    outer_value: Option<OuterValue<T>>,
+
+    /// The amount was held as a deposit for storing this structure.
+    domain_deposit: BalanceOf<T>,
+    /// The amount was held as a deposit for storing outer value.
+    outer_value_deposit: BalanceOf<T>,
+}
+
+pub struct WhoAndWhen {
+    account: AccountId,
+    block: BlockNumber,
+    time: Moment,
+}
+
+pub enum InnerValue {
+    Account(AccountId),
+    Space(SpaceId),
+    Post(PostId),
+}
+```
+
+## JS Examples
+
+### Top Level Domains
+The domains pallet will have a list of supported TLDs. This list can be fetched
+the following script.
+```javascript
+async function supportedTlds()  {
+    const tldEntries = await api.query.domains.supportedTlds.entries();
+    return tldEntries
+        .filter(([_, isSupported]) => isSupported)
+        .map(([key, _]) => key.args[0].toHuman());
+}
+```
+
+### Fetching the domain owner.
+In many scenarios we may want to resolve a domain name
+to the owner of this domain. This can be done by the following script.
+```javascript
+async function fetchDomainOwner(domain) {
+    const domainMeta = await api.query.domains.registeredDomains(domain);
+    return domainMeta.unwrap().owner;
+}
+```