Update trajectory.md

doc/trajectory.md

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 Modeling of Trajectories {#trajectories}
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+Here, we describe the final modeling problem in our composite workflow, how to build models of trajectory models using IMP.
+
 # Trajectory modeling step 1: gather information {#trajectories1}
 
 # Trajectory modeling step 2: representation, scoring, and search process {#trajectories2}
 
-Now, we have snapshot models for various intermediate states along our process of interest. In this step, we will combine these snapshot models to produce trajectories, as described in full [here](https://www.biorxiv.org/content/10.1101/2024.08.06.606842v1.abstract).
+Trajectory modeling connects alternative snapshot models at adjacent time points, followed by scoring the trajectories based on their fit to the input information, as described in full [here](https://www.biorxiv.org/content/10.1101/2024.08.06.606842v1.abstract).
 
 ## Background behind integrative spatiotemporal modeling