Tried to install with yarn

[pwFoo]

Tried to install as shown in readme file, but get an error message

/theia-php-extension # yarn --verbose rebuild:browser
yarn run v1.12.3
verbose 1.353 Checking for configuration file "/theia-php-extension/.npmrc".
verbose 1.356 Checking for configuration file "/usr/local/share/.npmrc".
verbose 1.36 Checking for configuration file "/usr/local/etc/npmrc".
verbose 1.362 Checking for configuration file "/root/.npmrc".
verbose 1.364 Checking for configuration file "/theia-php-extension/.npmrc".
verbose 1.37 Checking for configuration file "/theia-php-extension/.yarnrc".
verbose 1.372 Checking for configuration file "/usr/local/share/.yarnrc".
verbose 1.374 Checking for configuration file "/usr/local/etc/yarnrc".
verbose 1.376 Checking for configuration file "/root/.yarnrc".
verbose 1.377 Checking for configuration file "/theia-php-extension/.yarnrc".
verbose 1.411 current time: 2019-01-18T07:07:30.602Z
$ theia rebuild:browser
/bin/sh: theia: not found
verbose 1.689 Error: Command failed with exit code 127.
    at MessageError.ExtendableBuiltin (/opt/yarn-v1.12.3/lib/cli.js:727:66)
    at new MessageError (/opt/yarn-v1.12.3/lib/cli.js:756:123)
    at /opt/yarn-v1.12.3/lib/cli.js:36897:15
    at Generator.throw (<anonymous>)
    at step (/opt/yarn-v1.12.3/lib/cli.js:304:30)
    at /opt/yarn-v1.12.3/lib/cli.js:317:13
    at process.internalTickCallback (internal/process/next_tick.js:77:7)
error Command failed with exit code 127.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.